The present disclosure relates to an organic EL (electroluminescence) display in which an organic EL phenomenon is utilized for light emission.
With the recent accelerated developments in information and communication industries, there has been a demand for display devices having high degrees of functions. Among others, organic EL devices paid attention to as next-generation display devices have the merits of not only a wide view angle and an excellent contrast but also rapid response, when used as a spontaneous light emitting type display device.
The materials used for light emitting layers and the like constituting an organic EL device are generally classified into low-molecular materials and high-molecular materials. Of both the materials, in general, the low-molecular materials are known to show higher luminous efficiency and longer service life.
In addition, organic films of low-molecular materials are formed by dry processes (vapor deposition process) such as vacuum deposition, while organic films of high-molecular materials are formed by wet processes (coating process) such as spin coating system, ink jet system or nozzle coating system, or by printing processes such as flexographic printing or offset printing.
The vacuum deposition process is advantageous in that it is unnecessary to dissolve the organic thin film forming material in solvent and, therefore, removal of solvent after film formation is not needed. In the vacuum deposition process, however, it is difficult to form different films in different areas by use of metal masks, and, particularly, high manufacturing costs are needed for fabrication of large-sized panels. Therefore, the vacuum deposition process has had difficulties in application to large-screen substrates and in adaptation to mass production. In view of this, the coating process in which the area of display screen can be enlarged comparatively easily has drawn attention.
In such circumstances, for example Japanese Patent Laid-open No. 2006-140434 discloses a display wherein a hole injection layer, a hole transport layer, a red light emitting layer and a green light emitting layer are formed by a wet process such as ink jet process on the basis of light emitting elements for each color, and a blue light emitting layer and the like are formed thereover as common layers by a vacuum deposition process. This structure eliminates the need for fine patterning of the blue light emitting layer, and, therefore, highly possibly permits enlargement of the display screen area.